JP5358620B2 - Radiography equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiographic device capable of preventing occurrence of an artifact due to an effect of a structure other than a structure of interest in a reconstructed tomographic image. <P>SOLUTION: The radiographic device reconstructs a tomographic image in a prescribed cross section of a subject from a plurality of projection images of a subject imaged by tomosynthesis imaging by cumulatively adding corresponding pixels so that a position of a structure of interest is in alignment, and includes: a similarity calculation means for calculating similarity between pixels on a reference projection image and pixels on respective projection images, cumulatively added to the same position on the tomographic image with one projection image as the reference projection image; a weighting coefficient calculation means for calculating a weighting coefficient so as to be larger as the similarity becomes higher for the respective pixels of the plurality of projection images; and a back projection processing means for reconstructing the tomographic image by cumulatively adding multiplication values of pixel values of the pixels of the plurality of projection images cumulatively added to the same position on the tomographic image and the weighting coefficients corresponding to them. <P>COPYRIGHT: (C)2013,JPO&amp;INPIT

Description

  The present invention relates to a radiation imaging apparatus that captures a plurality of projection images (radiation images) by tomosynthesis imaging, and reconstructs a tomographic image at a predetermined cross section of a subject from the plurality of projection images thus captured.

  In tomosynthesis imaging, for example, a patient is irradiated with radiation at different angles while moving the radiation source in one direction, and the radiation that has passed through the subject is detected by a radiation detector. The projected images are taken continuously. Then, the tomographic images in the predetermined cross section of the subject are reconstructed by shifting the plurality of photographed projection images so that the positions of the structures of interest match and superimposing corresponding pixels.

  In tomosynthesis imaging, by utilizing the fact that structures overlap in the projection image depending on the imaging angle, as described above, by adding the projection image while appropriately shifting the target structure on the desired tomographic plane, An enhanced image (tomographic image) is obtained.

  However, in tomosynthesis imaging, the range of imaging angles is limited, so that the separation capability in the depth direction is limited, and artifacts due to the influence of structures other than the target structure may occur in the reconstructed tomographic image. There is a problem.

  Here, as a prior art document considered to be relevant to the present invention, Patent Document 1 discloses that one image is 4 × 6 pixels (in order to measure the amount of movement from two subject images). It is described that the image is divided into small regions for each pixel) and the similarity between two images is calculated for each small region. Patent Document 2 describes that a sub-region in a search region having high similarity to image data in a template is determined using a normalized cross-correlation method.

Japanese Patent Laid-Open No. 5-49631 JP-A-7-37074

  An object of the present invention is to provide a radiographic apparatus capable of preventing artifacts due to the influence of a structure other than the target structure in a tomographic image after reconstruction.

In order to achieve the above object, the present invention performs cumulative addition of corresponding pixels of a plurality of projection images of a subject imaged by tomosynthesis imaging so that the position of a target structure is aligned. A radiography apparatus for reconstructing a tomographic image at a predetermined cross section of an examiner,
Using one projection image as a reference projection image, the similarity between the pixel on the reference projection image and the pixel on each projection image, which is cumulatively added to the same position on the tomographic image, is calculated. Similarity calculation means;
For each pixel of the plurality of projected images, a weighting coefficient calculating means for calculating a weighting coefficient so as to increase as the similarity increases,
The inverse of reconstructing the tomographic image by cumulatively adding the pixel values of the plurality of pixels of the projection image and the corresponding weighting coefficients that are cumulatively added at the same position on the tomographic image. A radiation imaging apparatus including a projection processing unit is provided.

  Here, the similarity calculation means calculates the similarity between the first region on the reference projection image and the second region on each projection image, which is cumulatively added to the same position on the tomographic image. It is preferable to calculate.

  Moreover, it is preferable that the said similarity calculation means uses the projection image image | photographed from the said subject's front directly among the said several projection images as the said reference | standard projection image.

Further, the present invention provides a predetermined cross section of the subject by cumulatively adding corresponding pixels of a plurality of projection images of the subject imaged by tomosynthesis imaging so that the target structure is aligned. A radiography apparatus for reconstructing a tomographic image,
Back projection processing means for reconstructing the tomographic image from a plurality of the projected images;
Similarity calculation means for calculating the similarity of pixels on the projection image between the plurality of projection images for the plurality of pixels on the projection image cumulatively added to the same position on the tomographic image;
For each pixel of the tomographic image, weighting coefficient calculating means for calculating a weighting coefficient so as to increase as the similarity increases,
A radiation imaging apparatus is provided, comprising: a multiplication processing unit that multiplies a pixel value of each pixel of the tomographic image and a weighting coefficient corresponding to the pixel value to create a multiplication processed image.

Here, the similarity calculation unit, the for a given area on the projection image of the plurality of accumulated summed at the same position on the tomographic image, a plurality of between the projected image, given on the projection image It is preferable that the similarity of the region is calculated.

  Further, it is preferable that the similarity calculation means calculates the similarity by a normalized cross correlation.

  Moreover, it is preferable that the weighting coefficient calculation means uses the similarity as the weighting coefficient.

  According to the present invention, since the pixel values are weighted according to the similarity between the projected images, the target structure is emphasized in the reconstructed tomographic image, and is also influenced by the structure other than the target structure. The generation of artifacts can be prevented.

It is a block diagram of one embodiment showing composition of a radiography apparatus of the present invention. (A) And (B) is a conceptual diagram of an example showing the mode at the time of reconstruction of a tomographic image by tomosynthesis imaging. It is a block diagram of a 1st embodiment showing composition of an image processing device. It is a conceptual diagram of an example showing the positional relationship between the structure imaged by tomosynthesis imaging and the structure in the projection image. It is a conceptual diagram of an example showing the mode at the time of reconstruction of a tomographic image. It is a conceptual diagram of an example showing the relationship between the position of a structure, the position of a radiation source, and a projection position on a projection image. It is a block diagram of 2nd Embodiment showing the structure of an image processing apparatus.

  Hereinafter, a radiation imaging apparatus of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

  FIG. 1 is a block diagram of an embodiment showing a configuration of a radiation imaging apparatus of the present invention. The radiography apparatus 10 shown in FIG. 1 performs tomosynthesis imaging of the subject 34 to capture a plurality of projection images (radiation images) with different imaging angles, and the subject 34 is obtained from the plurality of projection images thus captured. A tomographic image in a cross section having a predetermined height is reconstructed. The radiation imaging apparatus 10 includes an imaging apparatus 12 and a console 14.

  The imaging device 12 performs tomosynthesis imaging of the subject 34 and captures a plurality of projection images having different imaging angles, and includes a radiation source 16, a radiation control device 18, and an imaging table 20. .

  The radiation source 16 irradiates a predetermined intensity of radiation for a predetermined period of time when a projection image of the subject 34 is captured under the control of the radiation control device 18. That is, a predetermined amount of radiation (dose) is irradiated.

  The radiation control device 18 controls the operation of the radiation source 16 (irradiation, irradiation position, irradiation angle, etc.) according to the imaging conditions by control of the control device 26 of the console 14 described later.

  The imaging table 20 in the illustrated example is a supine position imaging table, and is a table for positioning the subject 34 when a projection image is captured. It should be noted that a standing position imaging stand can be used as the imaging stand 20. A radiation detector 22 is disposed below the imaging table 20.

  The radiation detector 22 is, for example, a flat panel type (FPD: flat panel detector), and detects the radiation irradiated from the radiation source 16 and transmitted through the subject 34. An image signal (image data) of the captured projection image is output.

  Subsequently, the console 14 controls the overall operation of the radiation imaging apparatus 10, and includes an input device 24, a control device 26, an image processing device 28, a recording device 30, and a display device 32. Yes.

  The input device 24 is for inputting various instructions such as shooting instructions and various information such as shooting conditions, and can be exemplified by a keyboard and a mouse.

  The control device 26 controls the operations of the radiation control device 18, the image processing device 28, the recording device 30, and the display device 32 based on various instructions and various information input via the input device 24.

  The image processing device 28 performs various types of image processing including image synthesis processing and filter correction processing on the plurality of projection images (image signals thereof) input from the radiation detector 22 under the control of the control device 26. A tomographic image (image signal) in a cross section having a predetermined height of the subject 34 is reconstructed and output.

  The recording device 30 records various types of information including tomographic images (image signals) output from the image processing device 28 under the control of the control device 26, and includes a hard disk, a CD-R, and a DVD-R. A printer or the like can be exemplified.

  The display device 32 displays various types of information including a tomographic image output from the image processing device 28 under the control of the control device 26, and may be a liquid crystal display or the like.

  Next, the operation of the radiation imaging apparatus 10 during tomosynthesis imaging will be described.

  In the radiography apparatus 10, when performing tomosynthesis imaging, the subject 34 is positioned on the imaging surface of the imaging table 20. Thereafter, when an instruction to start photographing is given from the input device 24, tomosynthesis photographing is started under the control of the control device 26.

  When imaging is started, the imaging apparatus 12 controls the radiation control apparatus 18 to change the irradiation angle of the radiation source 16 in the direction of the subject 34 while moving the radiation source 16 in one direction to perform different irradiation. Radiation is irradiated to the subject 34 at an angle, and a plurality of projection images with different shooting angles are sequentially shot by one shooting operation. Each time a projection image of the subject 34 is captured, an image signal of the captured projection image is output from the radiation detector 22.

  At this time, in the console 14, image signals of a plurality of projection images input from the imaging device 12 are sequentially stored in the recording device 30 under the control of the control device 26.

  When the photographing is finished, the control device 26 controls the image composition processing or filter for aligning and superimposing the plurality of projection images from the image signals of the plurality of projection images having different photographing angles stored in the recording device 30. Various kinds of image processing including correction processing and the like are performed, and a tomographic image at a predetermined cross section of the subject 34 is reconstructed. The reconstructed tomographic image is displayed on the display device 32, and the image signal is recorded in the recording device 30 as necessary.

  Hereinafter, the operation at the time of tomographic image reconstruction will be described.

  A shift addition method is typically used as a tomographic image reconstruction method. In the shift addition method, based on the position of the radiation source 16 at the time of capturing each projected image, the positions of the captured images are sequentially shifted so that the corresponding structures are aligned so that the corresponding pixels are obtained. It is to add.

  FIGS. 2A and 2B are conceptual diagrams illustrating an example of a state when a tomographic image is reconstructed by tomosynthesis imaging. As shown in FIG. 6A, at the time of tomosynthesis imaging, the radiation source 16 starts from the position S1 and moves to S3, and the subject 34 is irradiated with radiation at each of the radiation source positions S1, S2, and S3. Assume that radiation images P1, P2, and P3 of the subject 34 are obtained.

  Here, it is assumed that the structures A and B exist at two positions where the height of the subject 34 is different as shown in FIG. At each imaging position (position of the radiation source 16 at the time of imaging) S1, S2, and S3, the radiation irradiated from the radiation source 16 passes through the subject 34 and enters the radiation detector 22. As a result, in the projection images P1, P2, and P3 corresponding to the photographing positions S1, S2, and S3, the two structures A and B are projected with different positional relationships.

  For example, in the case of the projection image P1, since the position S1 of the radiation source 16 is located on the left side of the structures A and B with respect to the moving direction of the radiation source 16, the structures A and B are respectively structures. Projected to the positions of P1A and P1B shifted to the right side of A and B. Similarly, in the case of the projection image P2, it is projected at the positions of P2A and P2B almost immediately below, and in the case of the projection image P3, it is projected at the positions of P3A and P3B shifted to the left side.

  When reconstructing a tomographic image in a cross section at a height where the structure A exists, the projection positions P1A, P2A, and P3A of the target structure A are matched based on the position of the radiation source 16, for example, FIG. As shown in (B), the projection image P1 is shifted to the left and the projection image P3 is shifted to the right to synthesize corresponding pixels. Thereby, a tomographic image having a height at which the target structure A exists is reconstructed. Similarly, a tomographic image in a cross section having an arbitrary height can be reconstructed.

  Next, image processing during tomographic image reconstruction in the image processing device 28 will be described.

  FIG. 3 is a block diagram of the first embodiment showing the configuration of the image processing apparatus. The image processing apparatus 28A shown in the figure includes a similarity calculation unit 36, a weighting coefficient calculation unit 38, and a back projection processing unit 40.

  The similarity calculation unit 36 uses one projection image out of a plurality of projection images captured by tomosynthesis imaging, for example, a projection image captured from directly in front of the subject as a reference projection image, on the tomographic image. A predetermined area in the vicinity of the pixel on the reference projection image (an M × N pixel area in the vicinity including the target pixel) and a predetermined area in the vicinity of the corresponding pixel on each projection image, which are cumulatively added to the same position The degree of similarity (or degree of dispersion) is calculated by a normalized mutual function.

  The weighting coefficient calculation unit 38 calculates the weighting coefficient so that each pixel of the plurality of projection images increases as the degree of similarity increases. Note that the weighting coefficient calculation unit 38 may use the similarity itself as a weighting coefficient.

  Then, the backprojection processing unit 40 cumulatively adds the multiplication values of the pixel values of the pixels on the plurality of projection images and the corresponding weighting coefficients, which are cumulatively added at the same position on the tomographic image, Reconstruct a tomographic image.

  The image processing device 28A accumulates and adds to the same position on the tomographic image at the time of reconstruction of the tomographic image, and a predetermined region near the pixel on the reference projection image and a predetermined pixel near the corresponding pixel on each projection image. Depending on the degree of similarity (correlation) between the regions, the pixel values of the corresponding pixels in each projection image are weighted and added to selectively emphasize the target structure in the focal plane (other than the focal plane) To suppress the structure).

  Here, as shown in FIG. 4, by tomosynthesis imaging, a plurality of projection images (three in the example of FIG. 4) of the subject including a star structure and a circular structure as target structures are obtained. Suppose it was filmed.

  As shown in FIG. 6, the coordinates of the structure of interest in a predetermined cross section of the subject 34 are (x, y, z), the positions of the radiation sources at the time of capturing the respective projection images (sxi, syi, szi), The projection position of the structure of interest on the i-th projection image Pi (i is an integer from −I to I, and the projection image taken from the front of the subject 34 is P0) (ti, si, 0) ), Assuming that the pixel value of each pixel of the projection image Pi is Pi (ti, si), the pixel value Tz (x, y) of each pixel of the tomographic image Tz after reconstruction by the conventional method is expressed by the following equation. The

  As a result of the above calculation, pixel information on each projection image Pi that has passed through a point (x, y, z) in space is cumulatively added to the pixel value Tz (x, y) of the corresponding pixel on the tomographic image Tz. Therefore, a tomographic image Tz in which the structure of the point (x, y, z) is emphasized can be obtained. For example, if the point (x, y, z) is one point on the star-shaped structure shown in FIG. 5, the projection information of the corresponding pixels of each projection image Pi acts so as to be superimposed. As a result, a tomographic image Tz in which the star-shaped structure is emphasized can be obtained.

  On the other hand, in the image processing device 28A, when the weighting coefficient for each pixel (ti, si) of each projection image Pi is wi (ti, si), the tomographic image Tz reconstructed by the back projection processing unit 40 is displayed. The pixel value Tz (x, y) of each pixel is expressed by the following equation.

  Here, in the image processing apparatus 28A, the weighting coefficient wi (ti, si) is calculated as follows.

  First, the similarity calculation unit 36 cumulatively adds the projection image P0 photographed from directly in front of the subject 34 among the plurality of projection images Pi to the same position on the tomographic image Tz as the reference projection image P0. , Between the neighboring rectangular area of the projection position P0 (t0, s0) of the pixel on the reference projection image P0 and the neighboring rectangular area of the projection position Pi (ti, si) of the corresponding pixel on each projection image Pi. Similarity is calculated by normalized cross-correlation.

  Then, the weighting coefficient calculation unit 38 calculates the weighting coefficient wi (ti, si) so that the higher the similarity is, the higher the degree of similarity is for each pixel of the plurality of projection images. Note that the weighting coefficient w0 (t0, s0) of the reference projection image P0 is “1” because of the normalized autocorrelation.

  The weighting by the weighting coefficient wi is performed based on the pixel value Tz (x, x, y) according to the similarity between the corresponding rectangular areas of the projection image Pi that are cumulatively added to the pixel value Tz (x, y) of each pixel of the tomographic image Tz. It acts to vary the contribution to y). Therefore, in the tomographic image Tz after reconstruction, it is possible to emphasize the target structure and prevent the occurrence of artifacts due to the influence of the structure other than the target structure.

  Note that the similarity calculation unit 36 accumulates and adds to the same position on the tomographic image Tz, not the predetermined area, and the pixel at the projection position P0 (t0, s0) on the reference projection image P0 and each projection image Pi. You may make it calculate the similarity with the pixel of the upper projection position Pi (ti, si). In addition, it is not essential to use a projection image taken directly in front of the subject as a reference projection image, and one projection image out of a plurality of projection images Pi may be used as a reference projection image.

  Further, it is not essential for the similarity calculation unit 36 to obtain the similarity between predetermined regions or pixels of two projection images by normalized cross-correlation, and the similarity between the two is obtained by various template matching (pattern matching). Can be calculated.

  The image processing device 28A reconstructs the tomographic image after weighting each pixel of each projection image, but is not limited to this, and weights each pixel of the tomographic image after reconstruction. The same effect can be obtained. Hereinafter, this case will be described.

  FIG. 7 is a block diagram of the second embodiment showing the configuration of the image processing apparatus. The image processing device 28B shown in the figure includes a back projection processing unit 42, a similarity calculation unit 44, a weighting coefficient calculation unit 46, and a multiplication processing unit 48.

  The back projection processing unit 42 reconstructs a tomographic image from a plurality of projection images.

  The similarity calculation unit 44 accumulates and adds to the same position on the tomographic image, and similarities between predetermined regions in the vicinity of the pixels on the plurality of projection images (the surrounding M × N pixel region including the target pixel). The degree is calculated by normalized cross correlation.

  The weighting coefficient calculation unit 46 calculates the weighting coefficient so that each pixel of the tomographic image increases as the degree of similarity increases.

  And the multiplication process part 48 produces the multiplication process image after a multiplication process by multiplying the pixel value of each pixel of a tomographic image, and the weighting coefficient corresponding to this. This multiplication processing image is displayed on the display device 32.

  The image processing device 28B responds to the tomographic image according to the similarity between predetermined regions in the vicinity of the pixels on the plurality of projection images, which are cumulatively added to the same position on the tomographic image after the reconstruction of the tomographic image. By weighting the pixel value of the target pixel, the target structure in the focal section is selectively emphasized (a structure other than the focal section is suppressed).

  In the image processing device 28B, assuming that the weighting coefficient for each pixel Tz (x, y) of the tomographic image Tz after reconstruction is wi (x, y), the pixel value Tz () of each pixel of the tomographic image Tz after reconstruction. x, y) is represented by the following formula.

  In the image processing device 28B, the weighting coefficient wi (x, y) is calculated as follows.

  First, the similarity between adjacent rectangular areas of the projection positions Pi (ti, si) of the pixels on the plurality of projection images Pi, which is cumulatively added to the same position on the tomographic image Tz by the similarity calculation unit 44, It is calculated by the average value of normalized cross-correlation between two images of a plurality of images.

  Then, the weighting coefficient calculation unit 46 calculates the weighting coefficient wi (x, y) so as to increase as the degree of similarity increases for each pixel of the tomographic image Tz.

  The weighting by the weighting coefficient wi is performed based on the pixel value Tz (x, x, y) according to the similarity between the corresponding rectangular areas of the projection image Pi that are cumulatively added to the pixel value Tz (x, y) of each pixel of the tomographic image Tz. It acts to vary the value of y). Therefore, it is possible to emphasize the structure of interest in the reconstructed tomographic image Tz with a smaller amount of calculation, and to prevent the occurrence of artifacts due to the influence of structures other than the structure of interest.

  Similarly, the similarity calculation unit 44 calculates the similarity between the pixels at the projection positions Pi (ti, si) on the plurality of projection images Pi that are cumulatively added to the same position on the tomographic image Tz. May be. Further, the similarity calculation unit 44 can calculate the similarity between predetermined regions or pixels of two projection images not only by normalized cross-correlation but also by various template matching (pattern matching).

  The radiographic apparatus of the above embodiment is an apparatus that captures a projection image of a subject by moving a radiation source along a linear trajectory by tomosynthesis imaging. However, the present invention is not limited to this, and for example, radiation For radiation imaging devices that perform tomosynthesis imaging by moving the radiation source in a trajectory other than a linear trajectory, such as moving the source in an arc-shaped trajectory centered on the subject and capturing a projected image of the subject Is also applicable. In this case, the present invention can be applied if the calculation formula for obtaining the corresponding pixel is changed according to the geometrical system of imaging.

  In addition, the radiographic apparatus of the above embodiment reconstructs a tomographic image at a predetermined cross section of the subject by a shift addition method. However, the present invention is not limited to this, for example, a filter back projection method. The present invention can also be applied to a radiation imaging apparatus that reconstructs a tomographic image by a reconstruction method other than the shift addition method, such as a method of accumulating the corresponding pixels to reconstruct a tomographic image. For example, in the case of a radiation imaging apparatus that reconstructs a tomographic image by a filter back projection method, the present invention can be applied using a projection image after filter processing.

The present invention is basically as described above.
Although the present invention has been described in detail above, the present invention is not limited to the above-described embodiment, and it is needless to say that various improvements and modifications may be made without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 10 Radiation imaging device 12 Imaging device 14 Console 16 Radiation source 18 Radiation control device 20 Imaging stand 24 Input device 26 Control device 28, 28A, 28B Image processing device 30 Recording device 32 Display device 34 Subject 36, 44 Similarity calculation part 38, 46 Weighting factor calculation unit 40, 42 Back projection processing unit 48 Multiplication processing unit

Claims (7)

A tomographic image at a predetermined cross section of the subject is reconstructed by accumulating the corresponding pixels of a plurality of projection images of the subject imaged by tomosynthesis imaging so that the position of the target structure is matched. A radiography apparatus,
Using one projection image as a reference projection image, the similarity between the pixel on the reference projection image and the pixel on each projection image, which is cumulatively added to the same position on the tomographic image, is calculated. Similarity calculation means;
For each pixel of the plurality of projected images, a weighting coefficient calculating means for calculating a weighting coefficient so as to increase as the similarity increases,
The inverse of reconstructing the tomographic image by cumulatively adding the pixel values of the plurality of pixels of the projection image and the corresponding weighting coefficients that are cumulatively added at the same position on the tomographic image. A radiation imaging apparatus comprising: a projection processing unit.   The similarity calculation means calculates a similarity between the first area on the reference projection image and the second area on each projection image, which is cumulatively added to the same position on the tomographic image. The radiographic apparatus according to claim 1.   The radiation imaging apparatus according to claim 1, wherein the similarity calculation unit uses, as the reference projection image, a projection image captured from directly in front of the subject among the plurality of projection images. A tomographic image at a predetermined cross section of the subject is reconstructed by accumulating the corresponding pixels of a plurality of projection images of the subject imaged by tomosynthesis imaging so that the position of the target structure is matched. A radiography apparatus,
Back projection processing means for reconstructing the tomographic image from a plurality of the projected images;
Similarity calculation means for calculating the similarity of pixels on the projection image between the plurality of projection images for the plurality of pixels on the projection image cumulatively added to the same position on the tomographic image;
For each pixel of the tomographic image, weighting coefficient calculating means for calculating a weighting coefficient so as to increase as the similarity increases,
A radiation imaging apparatus comprising: multiplication processing means for multiplying a pixel value of each pixel of the tomographic image and a weighting coefficient corresponding to the pixel value to create a multiplication processed image. The similarity calculation unit is configured to calculate a predetermined area on the projection image between the plurality of projection images for a predetermined area on the plurality of projection images cumulatively added to the same position on the tomographic image . The radiation imaging apparatus according to claim 4, wherein the similarity is calculated.   The radiation imaging apparatus according to claim 1, wherein the similarity calculation unit calculates the similarity by normalized cross-correlation.   The radiation imaging apparatus according to claim 1, wherein the weighting coefficient calculation unit uses the similarity as the weighting coefficient.

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